Abstract
The seeds of many legume species including soybean, Pongamia pinnata and the model legume Medicago truncatula store considerable oil, apart from protein, in their cotyledons. However, as a group, legume storage strategies are quite variable and provide opportunities for better understanding of carbon partitioning into different storage products. Legumes with their ability to fix nitrogen can also increase the sustainability of agricultural systems. This review integrates the cell biology, biochemistry and molecular biology of oil body biogenesis before considering biotechnology strategies to enhance oil body biosynthesis. Cellular aspects of packaging triacylglycerol (TAG) into oil bodies are emphasized. Enhancing seed oil content has successfully focused on the up-regulation of the TAG biosynthesis pathways using overexpression of enzymes such as diacylglycerol acyltransferase1 and transcription factors such as WRINKLE1 and LEAFY COTYLEDON1. While these strategies are central, decreasing carbon flow into other storage products and maximizing the packaging of oil bodies into the cytoplasm are other strategies that need further examination. Overall there is much potential for integrating carbon partitioning, up-regulation of fatty acid and TAG synthesis and oil body packaging, for enhancing oil levels. In addition to the potential for integrated strategies to improving oil yields, the capacity to modify fatty acid composition and use of oil bodies as platforms for the production of recombinant proteins in seed of transgenic legumes provide other opportunities for legume biotechnology.
Highlights
Legume seeds store proteins, lipids and starch required for energy and growth upon germination
As a group, legume storage strategies are quite variable and provide opportunities for better understanding of carbon partitioning into different storage products
Enhancing seed oil content has successfully focused on the up-regulation of the TAG biosynthesis pathways using overexpression of enzymes such as diacylglycerol acyltransferase1 and transcription factors such as WRINKLE1 and LEAFY COTYLEDON1
Summary
Lipids and starch required for energy and growth upon germination. The proportion of these storage components varies according to species (Table 1; Fig. 1). Legume seed can accumulate considerable oil aside from protein, and the oil content is largely dependent on legume species (Table 1). Pongamia pinnata (Pongamia) seed commonly stores 35% oil, which offers a potential source for biofuel use (Scott et al 2008). Biodiesel demand for future energy relies on greater seed oil production. Improvement of seed oil production will be important in addressing these challenges (Roesler et al 2016). Legumes are second to cereals in agricultural importance, based on area harvested and total production (Gepts et al 2005).
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